The overall objectives of the proposed research are to elucidate the mechanism, structure and mode of regulation of the enzyme, nitrate reductase and the relationship of this regulation to other cellular processes. Specific objectives of the proposed research are to study the molecular properties (molecular weight, quaternary structure, prosthetic groups, etc.) of the enzyme; determine the function and arrangement of the prosthetic groups, FAD, heme and molybdenum; determine the kinetic mechanism; determine the mechanism of inactivation of nitrate reductase through EPR studies; determine the intracellular location; and to study the possible role of cyanide as a physiological regulatory of nitrate reductase activity.